Transmission lines are important elements in circuit applications. For example, transmission lines typically provide the on-chip interconnect between active and passive devices of circuits, and are also utilized as impedance matching elements. A microstrip line is a type of transmission line widely utilized in microwave integrated circuit applications. Specifically, a microstrip line is a type of electrical transmission line that can be fabricated using printed circuit board technology, and may be used to convey microwave-frequency signals. Microwave components such as antennas, couplers, filters, power dividers, etc. can be formed from microstrip lines, the entire device existing as the pattern of metallization on a substrate.
Generally, microstrip lines comprise a signal line over a ground plane, which may be a solid metal plane, with a dielectric layer or layers separating the signal line from the ground plane. The ground plane has the advantageous feature of isolating the signal line from the substrate. Therefore, any substrate-induced losses are reduced. However, the formation of the ground plane also incurs drawbacks. As the scaling of back end of the line (BEOL) processes continues to trend downward, the vertical distance between the signal line and the ground plane becomes significantly smaller. This requires the signal line to be increasingly narrower in order to achieve the desired characteristic impedance. Consequently, insertion losses in microstrip lines become increasingly more significant, and demand better impedance matching between microstrip lines and network devices. Furthermore, the ground plane becomes a barrier for tuning the characteristic impedance of microstrip lines. This is due to the limited vertical distance between the signal line and the ground plane (i.e., a smaller distance with little room for tuning).
Moreover, the on-chip interconnect is one of the most significant factors that limit chip performance. Therefore, in a high performance integrated circuit design, an accurate model of the on-chip transmission line is needed for proper design. For example, in complementary metal-oxide-semiconductor (CMOS) technology, the effect of low resistivity silicon substrate coupling to the microstrip lines increases the on-chip transmission line insertion loss. Therefore, the substrate coupling should be taken into consideration in the modeling of any microstrip line implemented in CMOS technology. However, conventionally there is no accurate tool available to model the substrate effect. Consequently, modeling errors due to the substrate effect may cause an inaccuracy of the characteristic impedance and attenuation of the on-chip transmission line. Additionally, for Millimeter Wave/Terahertz applications the conventional on-chip interconnects suffer from reflections due to impedance mismatch that impact the signal integrity.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.